The iBiquity Digital Corporation HID Radio™ system is designed to permit a smooth evolution from current analog amplitude modulation (AM) and frequency modulation (FM) radio systems to an in-band on-channel (IBOC) system. An IBOC system can deliver digital audio and data services to mobile, portable, and fixed receivers from terrestrial transmitters in the existing medium frequency (MF) and very high frequency (VHF) radio bands.
IBOC signals can be transmitted in a hybrid format that includes an analog modulated carrier in combination with a plurality of digitally modulated subcarriers, or in an all-digital format in which an analog modulated carrier is not used. Using the hybrid format, broadcasters may continue to transmit analog AM and FM simultaneously with higher-quality and more robust digital signals, allowing themselves and their listeners to convert from analog to digital radio while maintaining their current frequency allocations. IBOC hybrid and all-digital waveforms are described in U.S. Pat. No. 7,933,368, which is incorporated by reference herein in its entirety.
Channel State Information (CSI) is useful in the decoding of digital signals in radio receivers. CSI as a signal-to-noise ratio (SNR) conveys the reliability of the associated digital symbols, while the estimation of complex channel gain and noise allows the demodulator to remove channel effects or compensate for them. Accurate CSI estimation can be important to reliably approximate Log-Likelihood Ratio (LLR) metrics and maximize reliable decoding performance. It is desirable to improve accuracy of CSI estimation for IBOC radio receivers.